1. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-1 Configuring Catalyst Switch Operations Identifying Problems That Occur in Redundant Switched Topologies

2. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-2 Outline Overview Redundant Switched and Bridged Topologies Broadcast Storms Multiple Frame Transmissions MAC Database Instability Summary

3. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-3 Redundant topology eliminates single points of failure. Redundant topology causes broadcast storms, multiple frame copies, and MAC address table instability problems. Redundant Topology

4. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-4 Host X sends a broadcast. Switches continue to propagate broadcast traffic over and over. Broadcast Storms

5. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-5 Host X sends a unicast frame to router Y. The MAC address of router Y has not been learned by either switch. Router Y will receive two copies of the same frame. Multiple Frame Copies

6. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-6 Host X sends a unicast frame to router Y. The MAC address of router Y has not been learned by either switch. Switches A and B learn the MAC address of host X on port 0. The frame to router Y is flooded. Switches A and B incorrectly learn the MAC address of host X on port 1. MAC Database Instability

7. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-7 Summary Bridged and switched networks are commonly designed with redundant links and devices, which can introduce problems such as broadcast storms, multiple frame transmission, and MAC database instability. A broadcast storm is created when each switch on a redundant network floods broadcast frames endlessly. Multiple frame transmissions occur when multiple copies of the same frame arrive at the intended host, potentially causing problems with the receiving protocol. MAC database instability occurs when multiple copies of a frame arrive on different ports of a switch.

8. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—1-8